Politely welcoming electronic doorbell

The politely welcoming electronic doorbell circuit is composed of the trigger control circuit, audio amplifier output circuit, music circuit, voice delay control circuit, and it is shown in Figure 3-122. Trigger control circuit is composed of the doorbell button S, magnetic switches SA, transistors V4, V5, resistors R3, R4, R6, diodes VD2, VD3, and capacitor..

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